Method of producing a silicone water-based elastomer

ABSTRACT

This invention describes a method of producing a silicone elastomer from an emulsion. When the ingredients are mixed together, the resulting latex can be used immediately. Removing the water from the latex results in a silicone elastomer. The method combines (A) an anionically stabilized, hydroxyl endblocked polydiorganosiloxane, present as an emulsion of dispersed particles in water, the emulsion having a pH of greater than 9, (B) dialkyltindicarboxylate, (C) alkylorthosilicate, (D) colloidal silica, and optionally (E) water, admixing (A) and (B) only in the presence of (C) to produce a dispersion of the ingredients in water. The ingredients can be distributed into a two-part system for storage. One embodiment includes fibers, lauryl alcohol, or a mixture of both in the emulsion; then forms an open-cell, elastomeric foam by forming a froth from the emulsion and removing the water from the froth.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of producing a silicone water-basedemulsion. After mixing the ingredients, the emulsion is immediatelycurable to an elastomer by removing the water at room temperature.

2. Background Information

Nelson, in Canadian Pat. No. 862,183, issued Jan. 26, 1971, teaches asilicone emulsion and process for treating fiberglass. His aqueousdispersion consists essentially of a liquid hydroxyl endblockeddimethylsiloxane polymer, a silane of the formula R_(n) SiR'_(4-n)wherein R is a hydrocarbon or substituted hydrocarbon radical, R' is ahydrolyzable radical other than halogen atoms, and n has a value of 0 or1, and a siloxane condensation catalyst.

In U.S. Pat. No. 2,843,555, issued July 15, 1958, Berridge teaches acomposition of hydroxyl endblocked polydiorganosiloxane, alkyl silicate,and metallic salt of an organic carboxylic acid. The alkyl silicate,which may be unhydrolyzed or hydrolyzed is of the formula ##STR1## whereR' may be OR. On mixing, the products immediately set up. Cure is withinone to two hours.

Cekada, in U.S. Pat. No. 3,355,406, issued Nov. 28, 1967, teachessilicone rubber latexes reinforced with a silsesquioxane. In his Example18, he shows a hydroxyl endblocked polydimethylsiloxane polymer,phenylsilsesquioxane, ethylorthosilicate, and dibutyltindilaurate. Thelatex was stated to form a fairly strong silicone rubber film whendeposited on a surface. The invention is stated as supplying a latexwhich is stable on storage.

Huebner and Meddaugh, in U.S. Pat. No. 3,706,695, issued Dec. 19, 1972,teach a method of preparing an emulsion which provides a heat stableelectrically conductive silicone rubber when the water is removed.According to their method, one emulsifies a hydroxyl endblockedpolydiorganosiloxane or polydiorganocyclosiloxane and polymerizes it,then adds carbon black, a metallic salt of a carboxylic acid, and asilane of the formula RSi(OR')₃. For long-term storage the emulsion iskept as a two-package system.

Fujiki, in Japanese Kokai No. 53-130752, laid open to public inspectionon Nov. 15, 1978, teaches an aqueous emulsion composed of 100 parts byweight of a hydroxyl endblocked polydiorganosiloxane, from 0.5 to 30parts by weight of silane containing at least 3 silicon-bondedhydrolyzable groups per molecule, curing catalyst, emulsifier, andwater. The composition is taught to have excellent storage stability atroom temperature and the property of converting to an elastomer bydrying at room temperature. Examples of curing catalysts are metal saltsof organic acids such as tin salts. There is no teaching concerning useof fillers.

Johnson et al., in U.S. Pat. No. 4,221,688, issued Sept. 9, 1980, teacha silicone emulsion having a dispersed phase of an anionicallystabilized hydroxylated polydiorganosiloxane and a colloidal silica anda continuous phase of water in which the pH is 9 to 11.5. Upon removalof the water at ambient conditions an elastomeric product is formed ifthe emulsion is stored for a period of time, as for 5 months, before thewater is removed. Addition of an organic tin compound reduces therequired storage time to a few days. The composition of Johnson et al.does not result in an elastomer if the water is removed immediately uponmixing of the ingredients.

Saam, in U.S. Pat. No. 4,244,849, issued Jan. 31, 1981, teaches anaqueous silicone emulsion which provides an elastomeric product uponremoval of the water. His emulsion comprises a continuous water phaseand an anionically stabilized dispersed silicone phase which is a graftcopolymer of a hydroxyl endblocked polydiorganosiloxane, and an alkalimetal silicate. An organic tin compound can be employed to acceleratethe formation of the graft copolymer. The Saam system does not usecolloidal silica as a necessary ingredient.

Laboratory tests have shown that when a silane having 3 hydrolyzablegroups is used in a composition containing liquid hydroxyl endblockedpolydimethylsiloxane, filler, and dibutyltindilaurate catalyst, thematerials did not cure when water was removed if the drying took placeimmediately after preparation of the mixture. Similar mixtures did notcure where the silane used was a partially hydrolyzed silane such asethylpolysilicate.

Bengtson, in U. S. Pat. No. 3,830,760, issued Aug. 20, 1984, discloses aprocess for the manufacture of a foamable composition which comprisesforming a mixture of a polymer or polymer precursor, curable on contactwith the atmosphere, and a polymer soluble inert blowing agent underpressure. His broad list of polymers includes silicone. His examplesshow polyurethanes which are mixed and then transferred to aerosolcontainers. Dispensing the ingredients from the container yields a frothwhich then cures from exposure to the atmosphere to produce aclosed-cell foam.

U.S. Pat. application, Ser. No. 665,224, filed Oct. 26, 1984, by Gravierand Kalinowski, assigned to the same assignee as the instantapplication, disclosed the use of fibers in silicone emulsions tostabilize a froth formed by dispersing air throughout the emulsion, thenremoving the water to yield an open-cell foam.

U.S. Pat. application Ser. No. 665,223, filed Oct. 26, 1984, now U.S.Pat. No. 4,559,369, by Bauman, Lee, and Rabe, assigned to the sameassignee as the instant application, disclosed a composition, undersuperatmospheric pressure, consisting of a silicone emulsion, aerosolpropellant, and optionally lauryl alcohol and optionally fibers. Whenreleased to atmospheric pressure at 25° C., a froth is produced whichforms an open-cell, elastomeric foam upon removal of water.

SUMMARY OF THE INVENTION

A method of producing silicone elastomer is disclosed. Combining theingredients yields an emulsion which can be immediately used to formcoatings on substrates or as caulking materials which cure to anelastomer upon removal of the water. The method combines (A) ananionically stabilized, hydroxyl endblocked polydiorganosiloxane,present as an emulsion of dispersed particles in water, the emulsionhaving a pH of greater than 9, (B) dialkyltindicarboxylate, (C)alkylorthosilicate of the formula Si(OR')₄ where R' is a lower alkylradical of from 1 to 4 carbon atoms inclusive, (D) colloidal silica, (E)optionally additional, water, and (F) optionally fibers and/or laurylalcohol. The emulsion is made by admixing (A) and (B) only when (C) ispresent, using sufficient amounts of the ingredients to yield 100 partsby weight of (A), from 0.1 to 2.0 parts by weight of (B), from 1 to 10parts by weight of (C), from 0 to 100 parts by weight of (D), optionally(E), and optionally from 1 to 10 parts by weight of the fibers of (F) orfrom 0.2 to 1.5 parts by weight of the lauryl alcohol of (F).

The emulsion of this invention has an extended shelf life because theingredients are combined just before use. They can be convenientlystored as a two-part emulsion which is combined before use. The emulsionformed by mixing the two parts can be used immediately upon mixing.There is no significant reaction time required between mixing and using,as is necessary in some systems. For instance, an emulsion ofanionically stabilized hydroxylated polydiorganosiloxanes and colloidalsilica, even in the presence of an organic tin compound, requires agestation period of several days before the emulsion will yield a curedelastomer upon the removal of the water.

When the method includes the optional addition of fine fibers or laurylalcohol or a mixture thereof, the combination can be stored as atwo-part emulsion which can be mixed together, then immediately formedinto a froth, either mechanically or through an aerosol means. Byremoving water from the froth, an open-cell, elastomeric foam isproduced.

DESCRIPTION OF THE INVENTION

This invention relates to a method of producing a silicone elastomerwhich is derived from ingredients comprising (A) 100 parts by weight ofan anionically stabilized, hydroxyl endblocked polydiorganosiloxanehaving a weight average molecular weight of above 50,000, the organicradicals being monovalent hydrocarbon radicals containing less thanseven carbon atoms per radical or 2-(perfluoroalkyl)ethyl radicalshaving less than seven carbon atoms per radical, present as an emulsionof dispersed particles in water, the emulsion having a pH of greaterthan 9, (B) from 0.1 to 2.0 parts by weight of dialkyltindicarboxylate,(C) from 1 to 10 parts by weight of alkylorthosilicate of the formulaSi(OR')₄ where R' is a lower alkyl radical of from 1 to 4 carbon atomsinclusive, (D) from 0 to 100 parts by weight of colloidal silica, (E)optionally additional water, and (F) optionally from 1 to 10 parts byweight of fibers having a diameter of from 1 to 10 micrometers and alength of from 30 micrometers to 10 millimeters with a length todiameter ratio of greater than 10 to 1, or from 0.2 to 1.5 parts byweight of lauryl alcohol, or mixtures thereof, consisting essentially ofadmixing the ingredients such that (A) and (B) are mixed only when (C)is present, to produce an emulsion of the ingredients dispersed inwater, which emulsion can be used immediately without a gestationperiod; and removing the water to produce the silicone elastomer.

A current commercial method of producing an aqueous silicone emulsionwhich, when dried, produces an elastomer comprises an anionicallystabilized hydroxylated polydiorganosiloxane and colloidal silica. Thisemulsion must age, for example for 5 months, before an elastomer isformed upon drying the emulsion. When this emulsion also contains anorganic tin compound as a catalyst, the aging period is reduced to amatter of several days, greater than 3 days for example. The propertiesof the elastomer formed by drying the emulsion are a function of the ageof the emulsion also. As the emulsion ages, the elongation, inparticular, decreases. The variability of the elastomer's elongationbecause of the age of the emulsion at the time of use, prohibits the useof the emulsion in applications which require a specific elongation.

A two-part emulsion produced by the method of this invention does notchange properties on shelf aging. The emulsion can be formulated toyield an elastomer having a given range of properties. The two parts canthen be shelf aged with no effect. When the two parts are mixed togetherand the emulsion is dried, the elastomer produced will have the physicalproperties for which it was formulated. An additional advantage is theability of the emulsion to be used immediately upon mixing; there is nowaiting period necessary. The mixed emulsion has a pot life of severaldays after mixing before it will begin to show a change of properties.At that time, the emulsion will have an appreciably increased viscositywhen compared to its viscosity immediately after mixing. A method ofproducing silicone open-cell, elastomeric foam from the two-partemulsion is disclosed. The method consists essentially of (1) mixingPart I and Part II to produce an emulsion of the ingredients dispersedin water, (2) immediately forming a froth of the mixture, then (3)immediately removing water from the froth to produce a foam. In thisembodiment, Part I consists essentially of 100 parts of (A), from 1 to10 parts of (D), and (F) from 1 to 10 parts by weight of fibers having adiameter of from 1 to 10 micrometers and a length of from 30 micrometersto 10 millimeters with a length to diameter ratio of greater than 10 to1, or from 0.2 to 1.5 parts by weight of lauryl alcohol, or mixturesthereof. Part II consists essentially of from 0.1 to 2.0 parts by weightof (B), from 1 to 10 parts by weight of (C), and from 15 to 35 parts byweight of (D).

The anionically stabilized, hydroxyl endblocked polydiorganosiloxaneemulsion used in this invention is a known material. The hydroxylendblocked polydiorganosiloxane (A) is one which can be emulsified,which imparts elastomeric properties to the product obtained after theremoval of the water from the emulsion, and which is anionicallystabilized. Tensile strengths and elongations at break improve withincreasing weight average molecular weight(Mw), with suitable tensilestrengths and elongations obtained above 50,000 Mw. The maximum weightaverage molecular weight is one which can be emulsified and which willgive elastomeric properties to the product obtained after the water isremoved from the emulsion. Weight average molecular weights up to about1,000,000 for the hydroxyl endblocked polydiorganosiloxane are expectedto be practical for this invention. The preferred Mw for the hydroxylendblocked polydiorganosiloxanes are in the range of 200,000 to 700,000.

The organic radicals of the hydroxyl endblocked polydiorganosiloxane canbe monovalent hydrocarbon radicals containing less than seven carbonatoms per radical and 2-(perfluoroalkyl)ethyl radicals including3,3,3-trifluoropropyl and 2-(perfluorobutyl)ethyl. The hydroxylendblocked polydiorganosiloxanes preferably contain organic radicals inwhich at least 50 percent are methyl. The hydroxyl endblockedpolydiorganosiloxanes are essentially linear polymers containing twoorganic groups per silicon atom but may include trace amcunts ofmonoorganosiloxane or triorganosiloxy units present as impurities of themanufacturing process. The preferred hydroxyl endblockedpolydiorganosiloxanes are the hydroxyl endblocked polydimethylsiloxanes.

The preferred anionically stabilized, hydroxyl endblockedpolydiorganosiloxanes are those prepared by the method of anionicemulsion polymerization described by Findlay et al. in U.S Pat. No.3,294,725, issued Dec. 27, 1966, which is hereby incorporated byreference to show the methods of polymerization, the ingredients used,and the hydroxyl endblocked polydiorganosiloxane obtained in anemulsion. Another method of preparing the anionically stabilized,hydroxyl endblocked polydiorganosiloxane is described by Hyde et al. inU.S. Pat. No. 2,891,920, issued June 23, 1959, which is herebyincorporated by reference to show the hydroxyl endblockedpolydiorganosiloxanes, the ingredients used, and their method ofpreparation. These methods and others are known in the art. The hydroxylendblocked polydiorganosiloxanes used in this invention are those whichare anionically stabilized. For the purpose of this invention"anionically stabilized" means the hydroxyl endblockedpolydiorganosiloxane is stabilized in emulsion with an anionicsurfactant. This silicone emulsion is in the form of an oil-in-wateremulsion, i.e., the polydiorganosiloxane is a dispersed phase ofparticles in a continuous phase of water.

Ingredient (B) is dialkyltindicarboxylate. The dialkyltindicarboxylatesare commercial materials. Preferred dialkyltindicarboxylates includedibutyltindiacetate, dibutyltindilaurate, and dioctyltindilaurate withdibutyltindilaurate most preferred. The dialkyltindicarboxylate can beused as is or it can be made into an emulsion. A suitable emulsion isproduced by emulsifying 50 percent by weight of thedialkyltindicarboxylate with water using about 10 percent by weight ofsodium alkylarylpolyether sulfonate as the emulsifying agent in any ofthe well known methods of producing oil-in-water emulsions.

Ingredient (C) is alkylorthosilicate. The alkylorthosilicate of theformula Si(OR')₄ is a commercially available material. R' is a loweralkyl radical of from 1 to 4 carbon atoms such as methyl, ethyl, propyl,isopropyl, and butyl. The preferred radicals are ethyl and normalpropyl. The silicate used in this invention is not a polymerizedmaterial such as ethylpolysilicate, which was found not usable in thisinvention. Materials such as methyltrimethoxysilane andphenyltrimethoxysilane were also found not usable because emulsions madewith these materials did not cure upon removal of the water.

Ingredient (D) is colloidal silica. Finely divided colloidal silicas arethose capable of being dispersed in the polydiorganosiloxane emulsion.The common forms of colloidal silica are commercially available ascolloidal silica dispersions in water, as dry powders of fumed silica orprecipitated silica, and the mined amorphous silicas that are known asdiatomaceous earth. Preferred are the commercially available colloidalsilica sols which are sodium stabilized, having a pH of greater than 10.These are sols of colloidal silica having surface areas varying fromabout 150 m² /g to about 750 m² /g and having solids contents from about15 percent to 50 percent in water. The colloidal silica acts as areinforcing agent to give improved physical properties. The method ofthis invention produces a silicone elastomer by removing the water froman emulsion produced by combining ingredients (A), (B), (C), andoptionally (D) in the amounts specified above. When combining theingredients, the polydiorganosiloxane (A) is mixed with thedialkyltindicarboxylate (B) only when the alkylorthosilicate (C) ispresent. Immediately after mixing (A), (B), and (C), an elastomer can beformed by removal of the water. The water can be removed at roomtemperature merely by exposing a layer of the mixture of (A), (B), and(C) to the atmosphere and allowing the water to evaporate. The timerequired for removal of the water is dependent upon the thickness of theemulsion layer. The evaporation rate can be increased by raising thetemperature or reducing the pressure or relative humidity of theatmosphere to which the emulsion is exposed. The elastomer obtained from(A), (B), and (C) is relatively weak because it contains noreinforcement. The addition of colloidal silica (D) results in anelastomer having improved physical properties, especially tensilestrength and elongation. The method of this invention can beconveniently practiced by combining the ingredients into two parts, PartI and Part II, and storing them as a two-part system. Part I and Part IIare then combined at the time of use. In order for the latex produced byadmixing Part I and Part II, according to the method of this invention,to be capable of being stored for long periods of time with no or littlechange of the properties of the elastomer produced, it is necessary thatthe polydiorganosiloxane (A) and the dialkyltindicarboxylate (B) arestored in separate parts. The other ingredients, (C) and (D) that areused in the latex can be stored in any combination in either or both ofPart I and Part II.

Preferred combinations are Part I consisting essentially of (A) and PartII consisting essentially of (B), (C), and (D); Part I consistingessentially of (A) and (C) and Part II consisting essentially of (B) and(D); Part I consisting essentially of (A) and (D) and Part II consistingessentially of (B) and (C); Part I consisting essentially of (A), (C),and (D) and Part II consisting essentially of (B). Most preferred arecombinations where Part I consists essentially of (A) and (C) and PartII consists essentially of (B) and (D), and where Part I consistsessentially of (A) and (D) and Part II consists essentially of (B) and(C).

The amounts of ingredients used in Part I and in Part II and the amountof Part I and Part II admixed together in the method of this inventionare such that the amount of ingredients in the latex produced by themethod are within the correct ranges. The amounts are based upon 100parts by weight of the hydroxyl endblocked polydiorganosiloxane (A). Theamount of dialkyltindicarboxylate (B) can vary from 0.1 to 2.0 parts byweight with the preferred amount being from 0.25 to 0.75 parts byweight. The amount of colloidal silica (D) can vary from 0 to 100 partsby weight with the preferred amount being from 1 to 50 parts by weightand most preferred from 5 to 50 parts by weight. The higher amounts ofcolloidal silica tend to give a higher hardness, higher tensilestrength, and lower elongation to the elastomer produced. The amount ofalkylorthosilicate (C) can vary from 1 to 10 parts by weight. Thepreferred amount is from 2 to 6 parts by weight where the organicradical is either ethyl or propyl.

A preferred method of this invention admixes 100 parts of anionicallystabilized, hydroxyl endblocked polydiorganosiloxane having a weightaverage molecular weight of greater than 200,000 in the form of anoil-in-water emulsion having a pH of greater than 9 and from 5 to 50parts by weight of colloidal silica in the form of a sodium stabilizedcolloidal silica dispersion in water and thickening agent to give PartI, the mixture having a pH of greater than 10. Part II is produced byadmixing from 0.25 to 0.75 part by weight of dibutyltindilaurate andfrom 2 to 6 parts by weight of either ethylorthosilicate or normalpropylorthosilicate. The Part I and Part II are stored separately untilready for use, then are combined to form a reinforced siliconeelastomeric latex. Sufficient thickener is used in Part I to give thelatex a viscosity of greater than 25 Pa·s at 25° C. The solids contentsof the emulsions used should be chosen so that the latex preferably hasa solids content of greater than 45 percent by weight, that is, thewater content of the latex is less than 55 percent by weight.

Another preferred method of this invention admixes 100 parts ofanionically stabilized, hydroxyl endblocked polydiorganosiloxane havinga weight average molecular weight of greater than 200,000 in the form ofan oil-in-water emulsion having a pH of greater than 9, from 2 to 6parts by weight of either ethylorthosilicate or normalpropylorthosilicate, and thickening agent to give Part I. Part II isproduced by admixing from 0.25 to 0.75 part by weight ofdibutyltindilaurate, and from 5 to 50 parts by weight of colloidalsilica in the form of a sodium stabilized colloidal silica dispersion inwater to give Part II, having a pH of greater than 10. Part I and PartII are stored separately until ready for use, then are combined to forma reinforced silicone elastomeric latex. Sufficient thickener is used inPart I to give the latex a viscosity of greater than 25 Pa·s at 25° C.The solids content of the emulsions used should be chosen so that thelatex preferably has a solids content of greater than 45 percent byweight.

When the ingredients are mixed together, the resulting final latex willform a silicone elastomer upon removal of the water. The properties ofthe elastomer can be modified by other ingredients which are added tothe emulsions, either into Part I or Part II or into their mixture,provided that the additional ingredients do not adversely effect theusefulness of the elastomer produced by removing the water from thelatex resulting from mixing of the ingredients according to the methodof this invention. Additives include additional emulsifiers andoptionally water, other fillers such as ground quartz or calciumcarbonate, heat stability additives such as iron oxide, pigments, andthickening agents. Fillers can be used to reduce the cost per unit ofthe elastomeric product or to make the emulsion useful as a caulkingmaterial. Thickening agents are useful for increasing the workingviscosity of the silicone emulsion to provide a material which can beused to coat a substrate with a film of elastomeric product. Suitablethickeners are available commercially and would be selected for theirstability and usability at a pH of 10 or greater. Useful thickenersinclude the classes of cellulose derivatives, alkali salts ofpolyacrylates and polymethylacrylates, sodium and ammonium salts ofcarboxylate copolymers and colloidal clays. The preferred thickeners arethe sodium salts of polyacrylates. Emulsifiers and water can be used toaid in the emulsification and mixing of the ingredients. For example,the dialkyltindicarboxylate is preferrably used as an emulsion. Thepreferred colloidal silica is a colloidal silica sol in water, but drypowders of colloidal silica can be dispersed in water.

The silicone latex produced by the method of this invention can containthe required ingredients over a wide range of concentrations to makeuseful products. Emulsions which have a low solids content can be usedfor imparting a property such as water repellency to a substrate such ascloth or paper by coating the substrate and drying it. Latexes of solidscontents such as above 45 percent by weight can be used to providethicker elastomeric films in coating applications such as roof coatings.When thicker coatings such as roof coatings are desired, it is alsopreferred to have latex viscosity of greater than 25 Pascal seconds at25° C. Latexes having solids content above about 45 percent by weightand a viscosity of greater than about 25 Pascal seconds producecontinuous, crack free dried films when applied to a substrate in a wetthickness on the order of 1.5 mm. Latexes having solids contents andviscosities below these values tend to crack upon drying when applied atthis thickness. Latexes having a solids content and viscositysufficiently high to produce a paste-type material are useful ascaulking material. The solids content is the percent of non-volatilematerial remaining in a 2 gram sample of the emulsion after it has beenheated for 1 hour at 150° C. in an air circulating oven. The sample isin an aluminum foil dish 60 mm in diameter and 15 mm deep.

An embodiment of the method of this invention can be used to produceopen-cell, elastomeric silicone foam. A foamable composition is producedby mixing Part I and Part II, immediately forming a froth of themixture, then immediately removing water from the froth to produce anopen-cell, elastomeric silicone foam. A preferred Part I consistsessentially of 100 parts of (A) (the hydroxyl endblockedpolydiorganosiloxane described above), 1 to 10 parts by weight of (D)(the colloidal silica sol described above), and (F) (from 1 to 10 partsby weight of the fibers or from 0.2 to 1.5 parts of lauryl alcohol ormixtures thereof). A preferred Part II consists essentially of from 0.1to 2.0 parts of (B) (the dialkyltindicarboxylate described above), from1 to 10 parts by weight of (C) (the alkylorthosilicate described above)and from 15 to 30 parts by weight of (D) (the colloidal silica describedabove).

The fibers or the lauryl alcohol, or mixtures thereof, are used toreinforce the walls of the cells formed when the froth is formed so thatthe froth is stable, i.e. the froth does not collapse. The fibers usedare fibers which are not adversely effected by the aqueous emulsion. Thefibers are more successfully dispersed into the emulsion if the averagediameter is less than 10 micrometers and their length is less than 10mm, preferably the diameter is less than 5 micrometers and the length isless than 8 mm. The smaller the diameter of the fibers and the shorterthey are, the easier they are to disperse. Glass fibers having adiameter of about 3 micrometers and an average length of about 4 mm arepreferred. The minimum diameter of useful fibers is about 1 micrometerand the minimum length of useful fibers is about 20 micrometers.Electrically conductive foams may be produced by using graphite fibersand graphite fibers coated with metal, such as nickel. A preferred rangeof fibers is from 4 to 8 parts of fiber per 100 parts by weight of (A).

It is believed that the fibers act as a froth stabilizer in that theyreinforce the walls of the cells as the froth is formed. The reinforcedcell walls do not collapse as the froth is dried, so that a foam isformed by drying the stabilized froth. The fibers also act as areinforcement in the foam cell walls so that the foam is stiffer andtougher than when the fibers are not present.

Lauryl alcohol also has been found to thicken the mixture of Part I andPart II and to stabilize the froth produced. The lauryl alcohol tends toproduce smaller cells and a softer foam. Lauryl alcohol has been foundto be unique in its ability to produce a uniform, small-celled froth.Mixtures of the fibers and the lauryl alcohol can be used to producefoam. A preferred combination is from 4 to 8 parts by weight of thefibers and from 0.5 to 1.0 part by weight of lauryl alcohol, based upon100 parts by weight of (A).

The mixture of Part I and Part II can be formed into a froth bymechanical means such as rapid stirring to whip in air, or by bubblingair or other gas through the mixture to create a froth. The froth can begenerated by using the known, commercial machines used to producemechanical foams.

The mixture of Part I and Part II can be formed into a froth by addingan aerosol propellant under superatmospheric pressure into the mixtureafter the mixture is placed into an aerosol container. From 1 to 20parts by weight of an aerosol propellant selected from the groupconsisting of isobutane, propane, dichlorodifluoromethane,trichlorofluoromethane, and mixtures thereof is added to the mixture inan aerosol propellant and mixed in. Discharging the mixture from thecontainer into a space at atmospheric pressure forms a froth because ofthe expansion of the aerosol propellant in the mixture. Because of thepresence of (F), the froth is stable. The water is then removed from thestable froth to form an open-celled, elastomeric silicone foam. There isno gestation period required in this method. The mixture can be producedand used immediately to form the froth and dried immediately to form afoam.

The aerosol propellant can be added to Part I in a first aerosolcontainer, and to Part II in a second aerosol container. The two can bestored in this form, then combined when it is desired to produce a foam.The mixture of first aerosol container and the mixture of second aerosolcontainer are combined in third container and mixed while still undersuperatmospheric pressure. After mixing, the combined mixture is thenimmediately discharged into a space at atmospheric pressure to form astable froth. Removing the water from the froth produces a foam.

A foam can also be produced in a continuous manner, as in a factorysituation, by pumping the ingredients of Part I into an aerosolcontainer, pumping the ingredients of Part II into a second aerosolcontainer, mixing the ingredients in each container, and continuouslypumping the mixed ingredients into a third container when Part I andPart II are mixed. The rate into and out of the containers are adjustedto maintain the ratio of ingredients shown above. The mixture from thethird container is continuously discharged to a space at atmosphericpressure, forming a stable froth in a continuous manner. The water iscontinuously removed from the froth to form a foam.

The stable froth produced by any of the above embodiments can have thewater removed by any suitable method, such as drying at roomtemperature, drying at elevated temperature, drying in a microwave oven,or by freezing the froth, then thawing and removing the water by dryingat room temperature. The method of removing the water is not criticalbecause the froth is stable enough to maintain itself as the water isremoved because of the composition used to form the froth.

The method of this embodiment produces an open-cell, elastomericsilicone foam which has good heat stability and weatherability whencompared to organic-based foams. The foam is useful as insulationcushioning, lightweight gap filler, and lightweight sealant. Whenelectrically conductive fibers are used, particularly when carbon blackis added to the formulation, the foam can be used as electricalconnectors or pressure switches.

The following examples are presented for purposes of illustrating theinvention and should not be construed as limiting the scope of theinvention which is properly delineated in the claims. All parts areparts by weight.

EXAMPLE 1

A two-part silicone elastomeric emulsion system was prepared.

Part I was an emulsion polymerized hydroxyl endblockedpolydimethylsiloxane having a weight average molecular weight of about325,000. The emulsion was prepared by mixing 54 parts of water, 100parts of low molecular weight linear hydroxyl-endblockedpolydimethylsiloxane, and 4 parts of a surfactant consisting of 30percent sodium lauryl sulphate. This mixture was homogenized, then mixedwith 1 part of dodecylbenzene sulfonic acid and allowed to polymerize.After polymerization, the emulsion was made basic by admixing 0.5 partof 50 percent aqueous diethylamine. The emulsion had a pH ofapproximately 10 and a solids content of about 63 percent by weight.

Part II was prepared by mixing 5 parts of ethylorthosilicate and 0.5part of dibutyltindilaurate.

An emulsion capable of curing at room temperature immediately afterpreparation was then prepared by mixing Part I and Part II. Immediatelyafter mixing, the resulting emulsion was de-aired, then poured into achase to give a wet sample with a thickness of 1.5 mm. After 7 days at77° F. and 50% relative humidity during which time the sample cured anddried, the elastomeric film was tested for physical properties inaccordance with ASTM D412 for tensile strength at break and elongationat break and with ASTM D624 die B for tear strength. The nonreinforcedelastomer, which did not contain colloidal silica, had a tensilestrength of 0.25 MPa, elongation of 253 percent, and tear strength of1.75 kN/M.

EXAMPLE 2

A two-part silicone elastomeric emulsion system having reinforcingfiller present was prepared.

A mixture (Part I) was prepared by mixing in a beaker with an air motor,100 parts of a dispersion of colloidal silica in water having 15 percentby weight colloidal silica, 2 parts of diethylamine, 172 parts of thepolydimethylsiloxane emulsion of Example 1 and 0.3 part of a siliconeantifoam emulsion having 30 percent by weight active ingredient. Themixture had a pH of greater than 10. A mixture (Part II) was prepared bymixing 5 parts of normal-propylorthosilicate and 0.5 part ofdibutyltindilaurate.

Parts I and II were then combined and mixed thoroughly. The mixture wasdeaired, then formed into a test sample as in Example 1. The test samplewas formed within 1 hour of the initial mixing of Part I and Part II.After curing and testing as in Example 1, the results were a tensilestrength of 1.43 MPa, elongation of 225 percent, and tear strength of11.7 kN/m.

EXAMPLE 3

Different crosslinking agents were evaluated.

Part I was prepared as in Example 2 except 9 parts of an emulsion of anacrylic thickening agent having 30 percent by weight solids was added asa last step.

Each Part II was prepared by mixing 5 parts of the crosslinking agentshown in Table I below with 0.5 part of dibutyltindilaurate. Parts I andII were then mixed, deaired, formed in test samples, cured, and testedas in Example 1. The results are shown in Table I.

The results show that this invention only cures properly when thecrosslinker is an alkylorthosilicate.

                  TABLE I                                                         ______________________________________                                                       Tensile                                                                       Strength Elongation                                                                              Tear Strength                               Crosslinker    MPa      Percent   kN/m                                        ______________________________________                                        normal-propylorthosilicate                                                                   3.14     548       21.2                                        ethylpolysilicate*                                                                           no cure                                                        methyltrimethoxysilane*                                                                      no cure                                                        phenyltrimethoxysilane*                                                                      no cure                                                        3-(2-aminoethylamino)*                                                                       no cure                                                        propyltrimethoxysilane                                                        ______________________________________                                         *Comparative example                                                     

EXAMPLE 4

A series of two part emulsions were prepared containing varying amountsand types of alkylorthosilicate crosslinker and varying amounts ofdibutyltindilaurate catalyst.

Part I was prepared as in Example 3.

Part II was prepared by mixing the type and amount of silicate shown inTable II below with the amount of catalyst shown. Comparative examplesusing alkylpolysilicate were also prepared.

Parts I and II were then mixed, de-aired, formed in test samples, curedand tested as in Example 1. The results are shown in Table II. Theminimum amount of catalyst necessary to produce a cure is dependent uponthe alkylorthosilicate used.

                  TABLE II                                                        ______________________________________                                                                      Tensile                                                              Catalyst Strength                                                                             Elongation                               Silicate    Amount   Amount   MPa    percent                                  ______________________________________                                        ethylpolysilicate*                                                                        3        1.0      No Cure                                         ethylpolysilicate*                                                                        5        0.5      No Cure                                         ethylpolysilicate*                                                                        5        1.0      No Cure                                         ethylorthosilicate                                                                        3        1.0      3.00   725                                      ethylorthosilicate                                                                        5        0.25     No Cure                                         ethylorthosilicate                                                                        5        0.5      3.56   860                                      ethylorthosilicate                                                                        5        0.75     3.17   750                                      ethylorthosilicate                                                                        5        1.0      2.86   610                                      normal propylortho-                                                                       3        0.25     1.65   300                                      silicate    3        0.5      4.41   830                                                  3        1.0      4.13   740                                                  5        0.0      No Cure                                                     5        0.25     2.48   590                                                  5        0.5      4.20   775                                                  5        1.0      3.96   760                                      ______________________________________                                         *Comparative example                                                     

EXAMPLE 5

A comparative example composition was prepared to illustrate thenecessity of the alkylorthosilicate.

A composition was prepared as in Part I of Example 2. To this was added0.5 part of dibutyltindilaurate catalyst. Sample of the catalyzedcomposition were tested for properties as in Example 1, preparing asample after aging the catalyzed composition for the time periods shownbelow before preparation of the sample for test. The results show thatthe composition does not yield a curable product until the compositionhas aged for a period of at least 5 days. Optimum properties are notreached until aging at least 9 days after catalyzation before samplepreparation.

    ______________________________________                                                     Tensile Strength                                                                           Elongation                                          Days Aging   MPa          Percent                                             ______________________________________                                        0            No Cure                                                          1            No Cure                                                          2            No Cure                                                          3            No Cure                                                          4            No Cure                                                          5            0.62         30                                                  7            0.76         50                                                  9            1.17         155                                                 ______________________________________                                    

EXAMPLE 6

The shelf life of the two-part composition was evaluated.

Two embodiments of a Part I were prepared by mixing 172 parts of thepolydimethylsiloxanes emulsion of Example 1, 10 parts of the thickeningagent of Example 3, and either 3 parts or 5 parts of normalpropylorthosilicate together to produce homogeneous emulsions.

Two embodiments of a Part II were prepared by mixing 100 parts of thecolloidal silica emulsion of Example 2 (15 parts of silica) with either0.25 part or 0.5 part of dibutyltindilaurate.

Portions of the two embodiments of Part I were mixed with the twoembodiments of Part II to give the parts of normal-propylorthosilicateand dibutyltindilaurate shown below in Table III. The 4 mixtures wereused to prepare samples as in Example 1. The samples were tested as inExample 1 with the results shown in Table III.

The remaining portions of the emulsions were aged at 23° C. for 6 monthsin sealed containers. Then they were mixed together, made into testsamples and tested as before. The results are shown in Table III.

                  TABLE III                                                       ______________________________________                                        Sample           A       B       C     D                                      ______________________________________                                        Normal-propylorthosilicate,                                                                    3       3       5     5                                      parts                                                                         Dibutyltindilaurate, part                                                                      0.25    0.5     0.25  0.5                                    Physical properties, after manufacture                                        Tensile Strength, MPa                                                                          2.55    2.76    2.69  2.46                                   Elongation, percent                                                                            739     748     624   633                                    Tear Strength, kN/m                                                                            20.0    17.5    17.7  17.5                                   Durometer, Shore A                                                                             52      52      60    59                                     Physical properties, after aging Parts A and Part B for 6 months              Tensile Strength, MPa                                                                          2.78    2.68    2.83  2.60                                   Elongation, percent                                                                            687     717     707   657                                    Tear Strength, kN/m                                                                            18.7    16.3    17.2  17.3                                   Durometer, Shore A                                                                             48      57      54    51                                     ______________________________________                                    

EXAMPLE 7

A series of compositions was prepared to evaluate the usefulness ofvarious colloidal silica emulsions.

Six embodiments of a Part I were prepared using three differentcolloidal silica emulsions at two different amounts each. Colloidalsilica A was a sol having 15 percent by weight of colloidal silicahaving a surface area of about 750 m² /g in water. Colloidal silica Bwas similar but was 30 percent by weight of a colloidal silica having asurface area of about 375 m² /g. Colloidal silica C was similar but was50 percent by weight of a colloidal silica having a surface area ofabout 150 m² /g.

Each of the six emulsions was prepared by mixing together the amount ofcolloidal silica solution shown in Table IV, 2 parts of diethylamine,172 parts of the polydimethylsiloxane emulsion of Example 1, and 0.5part of the antifoam of Example 2. Each had a pH of greater than 10.

Four embodiments of a Part II were prepared by mixing together theamounts of normal-propylorthosilicate and dibutyltindilaurate shown inTable IV.

Each embodiment of Part I was then mixed with each of the embodiments ofPart II as shown in Table IV, giving a total of 24 mixtures Theviscosity of each mixture was measured at room temperature with theresults shown in Table IV. Each mixture was then prepared into a testsample, dried, and cured, then tested as in Example 1. The results areshown in Table IV.

The quality of the films obtained upon curing was observed and judgedwith the results shown in Table IV, using a scale from 1 to 10. A ratingof 1 means the film had severe shrink cracking with large open fissures.A rating of 5 was heavy check cracking. A rating of 10 was crack free.It can be seen that the mixtures with the highest viscosities and solidscontents produced the best films. Those mixtures having a solids contentof below about 55 percent and a viscosity of below about 25 Pa·s did notproduce crack free films. The physical property valves shown for thefilms having cracks were obtained by carefully cutting the test piecesso that they contained a minimum number of flaws. The viscosity is feltto be the most important of these variables in obtaining good films upondrying and curing the emulsion.

                                      TABLE IV                                    __________________________________________________________________________    Run            1   2   3   4   5   6   7   8   9   10  11  12                 __________________________________________________________________________    Colloidal Silica A                                                                           67  67  67  67  100 100 100 100                                Colloidal Silica B                             33.3                                                                              33.3                                                                              33.3                                                                              33.3               Normal-propylorthosilicate                                                                   3   5   3   5   3   5   3   5   3   5   3   5                  Dibutyltindilaurate                                                                          0.25                                                                              0.5 0.5 0.25                                                                              0.25                                                                              0.5 0.5 0.25                                                                              0.25                                                                              0.5 0.5 0.25               Viscosity, Pa · s                                                                   15  15  15  15  10  0   10  10  35  30  32  35                 Film Rating    6   3   8   5   3   3   2   4   10  10  10  10                 Solids Content, Percent                                                                      48  48  48  48  44  44  44  44  56  56  56  56                 Silica Content, Parts                                                                        10  10  10  10  15  15  15  15  10  10  10  10                 Tensile Strength, MPa                                                                        1.77                                                                              1.58                                                                              1.86                                                                              2.62                                                                              2.55                                                                              1.07                                                                              1.9 1.55                                                                              2.82                                                                              1.63                                                                              1.61                                                                              1.54               Elongation, Percent                                                                          793 702 740 793 660 53  550 983 620 873 1097                                                                              710                __________________________________________________________________________    Run            13  14  15  16  17  18  19  20  21  22  23  24                 __________________________________________________________________________    Colloidal Silica B                                                                           33.3                                                                              66.7                                                                              66.7                                                                              66.7                                               Colloidal Silica C             30  30  30  30  60  60  60  60                 Normal-propylorthosilcate                                                                    3   5   3   5   3   5   3   5   3   5   3   5                  Dibutyltindilaurate                                                                          0.25                                                                              0.5 0.5 0.25                                                                              0.25                                                                              0.5 0.5 0.25                                                                              0.25                                                                              0.5 0.5 0.25               Viscosity Pa · s                                                                    18  18  18  18  72  70  70  78  68  60  65  75                 Film Rating    1   1   2   1   10  10  10  10  10  10  10  10                 Solids Content, Percent                                                                      52.3                                                                              52.3                                                                              52.3                                                                              52.3                                                                              59  59  59  59  58  58  58  58                 Silica Content, Parts                                                                        20  20  20  20  15  15  15  15  30  30  30  30                 Tensile Strength, MPa                                                                        --  1.53                                                                              1.58                                                                              0.86                                                                              1.31                                                                              1.45                                                                              1.83                                                                              0.90                                                                              2.74                                                                              3.03                                                                              1.46                                                                              2.85               Elongation, Percent                                                                          --  415 400 150 815 647 1058                                                                              807 1097                                                                              943 577 840                __________________________________________________________________________    Part I                             Part II                                    __________________________________________________________________________    Polydiorganosiloxane Emulsion                                                                      172                                                                              parts by weight                                                                          Normal-propylorthosilicate                                                                     as shown above            Antifoam             0.5                                                                              Dibutyltindilaurate                                                                      as shown above                             Acrylic Thickener    5                                                        Diethylamine         2                                                        Colloidal Silica        as shown above                                        __________________________________________________________________________

EXAMPLE 8

A two-part composition useful in producing foam was prepared.

Part I was prepared by mixing together 13.67 g of the colloidal silicadispersion of Example 2 (15 percent by weight silica), 3.0 g of a 50percent by weight solution of diethylamine, 290.19 g of the emulsionpolymerized hydroxyl endblocked polydimethylsiloxane (58 percent byweight polymer) of Example 1, 9.08 g of glass fibers having a diameterof about 2.6 to 3.8 micrometers and a length of less than 8 mm with anaverage length of about 4 mm, 1.51 g of lauryl alcohol, and 3.07 g of a30 percent by weight acrylic thickener solution. This composition had asolids content of about 58 percent by weight. Part II was prepared bymixing 8.51 g of normal-propylorthosilicate, 1.06 g of a 50 percent byweight solution of dibutyltindilaurate, 192.1 g of the colloidal silicadispersion in Part I above, 8.58 g of a 35 percent by weight solution ofdisodium N-octadecylsulfosuccinamate, and 6 g of the acrylic thickenersolution of Part I above.

Part I and Part II were combined in a mixer and mixed until uniform. A75 g portion was removed and placed into an aerosol container and avalve applied. The container was charged with 6 ml of isobutanepropellant and then shook to mix the propellant with the emulsion. Theremainder of the emulsion was mechanically frothed by mixing rapidly inthe mixer (a kitchen-type mixer having vertical beaters) for 10 minutesuntil sufficient air was beaten into the mixture to give a froth. Thefroth was then transferred to paper cups and cured by removing thewater. The first cup was allowed to dry at room temperature. The secondcup was frozen for 24 hours at 0° F., then dried at 70° F. for 4 days.The third cup was placed in a microwave oven set at low heat for 15minutes.

The emulsion in the aerosol container was discharged into 3 cups,forming a froth upon discharge. These 3 cups of froth were cured in thesame manner as described above for the mechanically formed froths.

Each of the cups of cured froth contained an open-cell, elastomericfoam. Samples of the foams were cut out and weighed to determine theirdensity. The results are shown in Table IV.

                  TABLE IV                                                        ______________________________________                                                    Density, kg/m.sup.3                                                             Mechanically                                                                              Aerosol                                             Cure          Formed Foam Formed Foam                                         ______________________________________                                        room temperature                                                                            134         61                                                  freeze, thaw  67          170                                                 microwave     51          37                                                  ______________________________________                                    

When compositions similar to this were prepared without the glass fiberand the lauryl alcohol to stabilize the froth so that it could be cured,the froth collapsed during cure at room temperature so that a foam wasnot obtained.

That which is claimed is:
 1. A method of producing a foam in which theingredients are stored before use as two parts, Part I consistingessentially of 100 parts by weight of an anionically stabilized,hydroxyl enblocked polydiorganosiloxane having a weight averagemolecular weight of about 50,000, the organic radicals being monovalenthydrocarbon radicals containing les than seven carbon atoms per radicalor 2-(perfluoroalkyl)ethyl radicals having less than seven carbon atomsper radical, present as an emulsion of dispsered particles in water, theemulsion having a pH of greater than 9 (A), from 1 to 10 parts by weightof (D), collodial silica and (F) from 1 to 10 parts by weight of fibershaving a diameter of from 1 to 10 micrometers and a length of from 30micrometers to 10 millimeters with a length to diameter ratio of greaterthan 10 to 1, or from 0.2 to 1.5 parts by weight of lauryl alcohol, ormixtures thereof, and Part II consisting essentially of 0.1 to 2.0 partsby weight of dialkyltindicarboxylate (B), from 1 to 10 parts by weightof (C) alkylorthosilicate of the formula Si(OR')4 where R' is a loweralkyl radical of from 1 to 4 carbon atoms inclusive, and from 15 to 35parts by weight of (D) colloidal slica; the method consistingessentially of (1) mixing Part I and Part II to produce an emulsion ofthe ingredients dispersed in water, (2) immediately forming a froth ofthe mixture, then (3) immediately removing water from the froth toproduce a foam.
 2. The method of claim 1 in which the froth is producedby mechanical stirring.
 3. The method of claim 1 in which (D) is presentas a collodial silica dispersion in water having a pH greater than 7 anda solids content of from 10 to 60 percent by weight.
 4. The curedsilicone elastomeric foam resulting from the method of claim 1.